Typical ring binder mechanisms have a plurality of rings for retaining loose-leaf pages, such as hole-punched pages, in a file or notebook. The rings can be selectively opened to add or remove pages from the ring binder mechanism or closed to retain the pages while allowing the pages to be moved along the rings. Each of the rings includes paired ring members mounted on adjacent hinge plates that are joined together about a pivot axis. A housing, which is typically metal and elongate, supports the hinge plates within the housing for pivotal movement relative to the housing about the pivot axis. Often, the housing is generally arch-shaped (e.g., U-shaped or C-shaped) in cross-section, with bent-under rims that hold the hinge plates within the housing.
The housing of the ring binder mechanism typically has an exposed metal outer surface. This exposed surface often contains nickel plating, to which some people may be sensitive. Additionally, it is difficult and costly to print on a metal surface particularly where the metal surface is nickel-plated. The process of nickel plating can also present some environmental and work hazard issues. Accordingly, it is known in some instances to replace the metal housing with a housing constructed from a polymeric material.
The housing, in an undeformed state, is slightly narrower than the joined hinge plates when the hinge plates are in a coplanar position. As the hinge plates pivot through this coplanar position, they deform the resilient housing laterally outwardly and cause a spring force in the housing to urge the hinge plates to pivot away from the coplanar position, either upward to open the rings or downward to close the rings. When the rings are closed, the spring force of the housing resists hinge plate movement and thereby holds the rings together. Similarly, when the rings are open, the spring force of the housing holds them apart. Typically, an operator can overcome the spring force of the housing by manually pulling the ring members of the rings apart or pushing them together.
Levers may be provided on one or both ends of the housing for pivoting the hinge plates and thereby moving the rings between their opened and closed positions. As illustrated in FIG. 1A, typical levers include an upper arm disposed adjacent the upper surface of the hinge plates and a lower arm disposed adjacent the lower surface of the hinge plates. As the lever is pivoted away from the housing (FIG. 1B), the lower arm contacts the lower surface of the hinge plates and drives the hinge plates upward through the coplanar position thereby opening the rings. To close the rings, the lever is pivot in the opposite direction (i.e., toward the housing) so that the upper arm contacts the upper surface of the hinge plates and drives the hinge plates downward through the coplanar position thereby closing the rings.
As illustrated in FIG. 1C, some prior art levers have been known to disengage during pivotal rotation of the lever to open the rings. As mentioned above, to open the rings, the lever is rotated away from the housing so that the lower arm of the lever contacts the hinge plates and drives them upward. In some prior art levers, if the user rotates the lever too far, the lower arm of the lever will rotate beyond the end of the hinge plate and disengage from the hinge plate. If this occurs, the lever can no longer be used to open or close the rings. Disengagement of the lever from the hinge plates is more likely to occur when the housing is constructed from a polymeric material than when it is constructed from a metal material because the polymeric housing is more flexible. The polymeric housing provides less resistance to the lever disengaging from the hinge plates.